# AWS Lambda Construct Library <!--BEGIN STABILITY BANNER--> ---   --- <!--END STABILITY BANNER--> This construct library allows you to define AWS Lambda Functions. ```ts const fn = new lambda.Function(this, 'MyFunction', { runtime: lambda.Runtime.NODEJS_12_X, handler: 'index.handler', code: lambda.Code.fromAsset(path.join(__dirname, 'lambda-handler')), }); ``` ## Handler Code The `lambda.Code` class includes static convenience methods for various types of runtime code. * `lambda.Code.fromBucket(bucket, key[, objectVersion])` - specify an S3 object that contains the archive of your runtime code. * `lambda.Code.fromInline(code)` - inline the handle code as a string. This is limited to supported runtimes and the code cannot exceed 4KiB. * `lambda.Code.fromAsset(path)` - specify a directory or a .zip file in the local filesystem which will be zipped and uploaded to S3 before deployment. See also [bundling asset code](#bundling-asset-code). * `lambda.Code.fromDockerBuild(path, options)` - use the result of a Docker build as code. The runtime code is expected to be located at `/asset` in the image and will be zipped and uploaded to S3 as an asset. The following example shows how to define a Python function and deploy the code from the local directory `my-lambda-handler` to it: [Example of Lambda Code from Local Assets](test/integ.assets.lit.ts) When deploying a stack that contains this code, the directory will be zip archived and then uploaded to an S3 bucket, then the exact location of the S3 objects will be passed when the stack is deployed. During synthesis, the CDK expects to find a directory on disk at the asset directory specified. Note that we are referencing the asset directory relatively to our CDK project directory. This is especially important when we want to share this construct through a library. Different programming languages will have different techniques for bundling resources into libraries. ## Docker Images Lambda functions allow specifying their handlers within docker images. The docker image can be an image from ECR or a local asset that the CDK will package and load into ECR. The following `DockerImageFunction` construct uses a local folder with a Dockerfile as the asset that will be used as the function handler. ```ts new lambda.DockerImageFunction(this, 'AssetFunction', { code: lambda.DockerImageCode.fromImageAsset(path.join(__dirname, 'docker-handler')), }); ``` You can also specify an image that already exists in ECR as the function handler. ```ts import * as ecr from '@aws-cdk/aws-ecr'; const repo = new ecr.Repository(this, 'Repository'); new lambda.DockerImageFunction(this, 'ECRFunction', { code: lambda.DockerImageCode.fromEcr(repo), }); ``` The props for these docker image resources allow overriding the image's `CMD`, `ENTRYPOINT`, and `WORKDIR` configurations. See their docs for more information. ## Execution Role Lambda functions assume an IAM role during execution. In CDK by default, Lambda functions will use an autogenerated Role if one is not provided. The autogenerated Role is automatically given permissions to execute the Lambda function. To reference the autogenerated Role: ```ts const fn = new lambda.Function(this, 'MyFunction', { runtime: lambda.Runtime.NODEJS_12_X, handler: 'index.handler', code: lambda.Code.fromAsset(path.join(__dirname, 'lambda-handler')), }); const role = fn.role; // the Role ``` You can also provide your own IAM role. Provided IAM roles will not automatically be given permissions to execute the Lambda function. To provide a role and grant it appropriate permissions: ```ts const myRole = new iam.Role(this, 'My Role', { assumedBy: new iam.ServicePrincipal('sns.amazonaws.com'), }); const fn = new lambda.Function(this, 'MyFunction', { runtime: lambda.Runtime.NODEJS_12_X, handler: 'index.handler', code: lambda.Code.fromAsset(path.join(__dirname, 'lambda-handler')), role: myRole, // user-provided role }); myRole.addManagedPolicy(iam.ManagedPolicy.fromAwsManagedPolicyName("service-role/AWSLambdaBasicExecutionRole")); myRole.addManagedPolicy(iam.ManagedPolicy.fromAwsManagedPolicyName("service-role/AWSLambdaVPCAccessExecutionRole")); // only required if your function lives in a VPC ``` ## Resource-based Policies AWS Lambda supports resource-based policies for controlling access to Lambda functions and layers on a per-resource basis. In particular, this allows you to give permission to AWS services and other AWS accounts to modify and invoke your functions. You can also restrict permissions given to AWS services by providing a source account or ARN (representing the account and identifier of the resource that accesses the function or layer). ```ts declare const fn: lambda.Function; const principal = new iam.ServicePrincipal('my-service'); fn.grantInvoke(principal); // Equivalent to: fn.addPermission('my-service Invocation', { principal: principal, }); ``` For more information, see [Resource-based policies](https://docs.aws.amazon.com/lambda/latest/dg/access-control-resource-based.html) in the AWS Lambda Developer Guide. Providing an unowned principal (such as account principals, generic ARN principals, service principals, and principals in other accounts) to a call to `fn.grantInvoke` will result in a resource-based policy being created. If the principal in question has conditions limiting the source account or ARN of the operation (see above), these conditions will be automatically added to the resource policy. ```ts declare const fn: lambda.Function; const servicePrincipal = new iam.ServicePrincipal('my-service'); const sourceArn = 'arn:aws:s3:::my-bucket'; const sourceAccount = '111122223333'; const servicePrincipalWithConditions = servicePrincipal.withConditions({ ArnLike: { 'aws:SourceArn': sourceArn, }, StringEquals: { 'aws:SourceAccount': sourceAccount, }, }); fn.grantInvoke(servicePrincipalWithConditions); // Equivalent to: fn.addPermission('my-service Invocation', { principal: servicePrincipal, sourceArn: sourceArn, sourceAccount: sourceAccount, }); ``` ## Versions You can use [versions](https://docs.aws.amazon.com/lambda/latest/dg/configuration-versions.html) to manage the deployment of your AWS Lambda functions. For example, you can publish a new version of a function for beta testing without affecting users of the stable production version. The function version includes the following information: * The function code and all associated dependencies. * The Lambda runtime that executes the function. * All of the function settings, including the environment variables. * A unique Amazon Resource Name (ARN) to identify this version of the function. You could create a version to your lambda function using the `Version` construct. ```ts declare const fn: lambda.Function; const version = new lambda.Version(this, 'MyVersion', { lambda: fn, }); ``` The major caveat to know here is that a function version must always point to a specific 'version' of the function. When the function is modified, the version will continue to point to the 'then version' of the function. One way to ensure that the `lambda.Version` always points to the latest version of your `lambda.Function` is to set an environment variable which changes at least as often as your code does. This makes sure the function always has the latest code. For instance - ```ts const codeVersion = "stringOrMethodToGetCodeVersion"; const fn = new lambda.Function(this, 'MyFunction', { runtime: lambda.Runtime.NODEJS_12_X, handler: 'index.handler', code: lambda.Code.fromAsset(path.join(__dirname, 'lambda-handler')), environment: { 'CodeVersionString': codeVersion, }, }); ``` The `fn.latestVersion` property returns a `lambda.IVersion` which represents the `$LATEST` pseudo-version. However, most AWS services require a specific AWS Lambda version, and won't allow you to use `$LATEST`. Therefore, you would normally want to use `lambda.currentVersion`. The `fn.currentVersion` property can be used to obtain a `lambda.Version` resource that represents the AWS Lambda function defined in your application. Any change to your function's code or configuration will result in the creation of a new version resource. You can specify options for this version through the `currentVersionOptions` property. NOTE: The `currentVersion` property is only supported when your AWS Lambda function uses either `lambda.Code.fromAsset` or `lambda.Code.fromInline`. Other types of code providers (such as `lambda.Code.fromBucket`) require that you define a `lambda.Version` resource directly since the CDK is unable to determine if their contents had changed. ### `currentVersion`: Updated hashing logic To produce a new lambda version each time the lambda function is modified, the `currentVersion` property under the hood, computes a new logical id based on the properties of the function. This informs CloudFormation that a new `AWS::Lambda::Version` resource should be created pointing to the updated Lambda function. However, a bug was introduced in this calculation that caused the logical id to change when it was not required (ex: when the Function's `Tags` property, or when the `DependsOn` clause was modified). This caused the deployment to fail since the Lambda service does not allow creating duplicate versions. This has been fixed in the AWS CDK but *existing* users need to opt-in via a [feature flag]. Users who have run `cdk init` since this fix will be opted in, by default. Existing users will need to enable the [feature flag] `@aws-cdk/aws-lambda:recognizeVersionProps`. Since CloudFormation does not allow duplicate versions, they will also need to make some modification to their function so that a new version can be created. Any trivial change such as a whitespace change in the code or a no-op environment variable will suffice. When the new logic is in effect, you may rarely come across the following error: `The following properties are not recognized as version properties`. This will occur, typically when [property overrides] are used, when a new property introduced in `AWS::Lambda::Function` is used that CDK is still unaware of. To overcome this error, use the API `Function.classifyVersionProperty()` to record whether a new version should be generated when this property is changed. This can be typically determined by checking whether the property can be modified using the *[UpdateFunctionConfiguration]* API or not. [feature flag]: https://docs.aws.amazon.com/cdk/latest/guide/featureflags.html [property overrides]: https://docs.aws.amazon.com/cdk/latest/guide/cfn_layer.html#cfn_layer_raw [UpdateFunctionConfiguration]: https://docs.aws.amazon.com/lambda/latest/dg/API_UpdateFunctionConfiguration.html ## Aliases You can define one or more [aliases](https://docs.aws.amazon.com/lambda/latest/dg/configuration-aliases.html) for your AWS Lambda function. A Lambda alias is like a pointer to a specific Lambda function version. Users can access the function version using the alias ARN. The `version.addAlias()` method can be used to define an AWS Lambda alias that points to a specific version. The following example defines an alias named `live` which will always point to a version that represents the function as defined in your CDK app. When you change your lambda code or configuration, a new resource will be created. You can specify options for the current version through the `currentVersionOptions` property. ```ts const fn = new lambda.Function(this, 'MyFunction', { currentVersionOptions: { removalPolicy: RemovalPolicy.RETAIN, // retain old versions retryAttempts: 1, // async retry attempts }, runtime: lambda.Runtime.NODEJS_12_X, handler: 'index.handler', code: lambda.Code.fromAsset(path.join(__dirname, 'lambda-handler')), }); fn.currentVersion.addAlias('live'); ``` ## Layers The `lambda.LayerVersion` class can be used to define Lambda layers and manage granting permissions to other AWS accounts or organizations. [Example of Lambda Layer usage](test/integ.layer-version.lit.ts) By default, updating a layer creates a new layer version, and CloudFormation will delete the old version as part of the stack update. Alternatively, a removal policy can be used to retain the old version: ```ts new lambda.LayerVersion(this, 'MyLayer', { removalPolicy: RemovalPolicy.RETAIN, code: lambda.Code.fromAsset(path.join(__dirname, 'lambda-handler')), }); ``` ## Architecture Lambda functions, by default, run on compute systems that have the 64 bit x86 architecture. The AWS Lambda service also runs compute on the ARM architecture, which can reduce cost for some workloads. A lambda function can be configured to be run on one of these platforms: ```ts new lambda.Function(this, 'MyFunction', { runtime: lambda.Runtime.NODEJS_12_X, handler: 'index.handler', code: lambda.Code.fromAsset(path.join(__dirname, 'lambda-handler')), architecture: lambda.Architecture.ARM_64, }); ``` Similarly, lambda layer versions can also be tagged with architectures it is compatible with. ```ts new lambda.LayerVersion(this, 'MyLayer', { removalPolicy: RemovalPolicy.RETAIN, code: lambda.Code.fromAsset(path.join(__dirname, 'lambda-handler')), compatibleArchitectures: [lambda.Architecture.X86_64, lambda.Architecture.ARM_64], }); ``` ## Lambda Insights Lambda functions can be configured to use CloudWatch [Lambda Insights](https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/Lambda-Insights.html) which provides low-level runtime metrics for a Lambda functions. ```ts new lambda.Function(this, 'MyFunction', { runtime: lambda.Runtime.NODEJS_12_X, handler: 'index.handler', code: lambda.Code.fromAsset(path.join(__dirname, 'lambda-handler')), insightsVersion: lambda.LambdaInsightsVersion.VERSION_1_0_98_0, }); ``` If the version of insights is not yet available in the CDK, you can also provide the ARN directly as so - ```ts const layerArn = 'arn:aws:lambda:us-east-1:580247275435:layer:LambdaInsightsExtension:14'; new lambda.Function(this, 'MyFunction', { runtime: lambda.Runtime.NODEJS_12_X, handler: 'index.handler', code: lambda.Code.fromAsset(path.join(__dirname, 'lambda-handler')), insightsVersion: lambda.LambdaInsightsVersion.fromInsightVersionArn(layerArn), }); ``` ## Event Rule Target You can use an AWS Lambda function as a target for an Amazon CloudWatch event rule: ```ts import * as events from '@aws-cdk/aws-events'; import * as targets from '@aws-cdk/aws-events-targets'; declare const fn: lambda.Function; const rule = new events.Rule(this, 'Schedule Rule', { schedule: events.Schedule.cron({ minute: '0', hour: '4' }), }); rule.addTarget(new targets.LambdaFunction(fn)); ``` ## Event Sources AWS Lambda supports a [variety of event sources](https://docs.aws.amazon.com/lambda/latest/dg/invoking-lambda-function.html). In most cases, it is possible to trigger a function as a result of an event by using one of the `add<Event>Notification` methods on the source construct. For example, the `s3.Bucket` construct has an `onEvent` method which can be used to trigger a Lambda when an event, such as PutObject occurs on an S3 bucket. An alternative way to add event sources to a function is to use `function.addEventSource(source)`. This method accepts an `IEventSource` object. The module __@aws-cdk/aws-lambda-event-sources__ includes classes for the various event sources supported by AWS Lambda. For example, the following code adds an SQS queue as an event source for a function: ```ts import * as eventsources from '@aws-cdk/aws-lambda-event-sources'; import * as sqs from '@aws-cdk/aws-sqs'; declare const fn: lambda.Function; const queue = new sqs.Queue(this, 'Queue'); fn.addEventSource(new eventsources.SqsEventSource(queue)); ``` The following code adds an S3 bucket notification as an event source: ```ts import * as eventsources from '@aws-cdk/aws-lambda-event-sources'; import * as s3 from '@aws-cdk/aws-s3'; declare const fn: lambda.Function; const bucket = new s3.Bucket(this, 'Bucket'); fn.addEventSource(new eventsources.S3EventSource(bucket, { events: [ s3.EventType.OBJECT_CREATED, s3.EventType.OBJECT_REMOVED ], filters: [ { prefix: 'subdir/' } ] // optional })); ``` See the documentation for the __@aws-cdk/aws-lambda-event-sources__ module for more details. ## Lambda with DLQ A dead-letter queue can be automatically created for a Lambda function by setting the `deadLetterQueueEnabled: true` configuration. ```ts const fn = new lambda.Function(this, 'MyFunction', { runtime: lambda.Runtime.NODEJS_12_X, handler: 'index.handler', code: lambda.Code.fromInline('exports.handler = function(event, ctx, cb) { return cb(null, "hi"); }'), deadLetterQueueEnabled: true, }); ``` It is also possible to provide a dead-letter queue instead of getting a new queue created: ```ts import * as sqs from '@aws-cdk/aws-sqs'; const dlq = new sqs.Queue(this, 'DLQ'); const fn = new lambda.Function(this, 'MyFunction', { runtime: lambda.Runtime.NODEJS_12_X, handler: 'index.handler', code: lambda.Code.fromInline('exports.handler = function(event, ctx, cb) { return cb(null, "hi"); }'), deadLetterQueue: dlq, }); ``` See [the AWS documentation](https://docs.aws.amazon.com/lambda/latest/dg/dlq.html) to learn more about AWS Lambdas and DLQs. ## Lambda with X-Ray Tracing ```ts const fn = new lambda.Function(this, 'MyFunction', { runtime: lambda.Runtime.NODEJS_12_X, handler: 'index.handler', code: lambda.Code.fromInline('exports.handler = function(event, ctx, cb) { return cb(null, "hi"); }'), tracing: lambda.Tracing.ACTIVE, }); ``` See [the AWS documentation](https://docs.aws.amazon.com/lambda/latest/dg/lambda-x-ray.html) to learn more about AWS Lambda's X-Ray support. ## Lambda with Profiling The following code configures the lambda function with CodeGuru profiling. By default, this creates a new CodeGuru profiling group - ```ts const fn = new lambda.Function(this, 'MyFunction', { runtime: lambda.Runtime.PYTHON_3_6, handler: 'index.handler', code: lambda.Code.fromAsset('lambda-handler'), profiling: true, }); ``` The `profilingGroup` property can be used to configure an existing CodeGuru profiler group. CodeGuru profiling is supported for all Java runtimes and Python3.6+ runtimes. See [the AWS documentation](https://docs.aws.amazon.com/codeguru/latest/profiler-ug/setting-up-lambda.html) to learn more about AWS Lambda's Profiling support. ## Lambda with Reserved Concurrent Executions ```ts const fn = new lambda.Function(this, 'MyFunction', { runtime: lambda.Runtime.NODEJS_12_X, handler: 'index.handler', code: lambda.Code.fromInline('exports.handler = function(event, ctx, cb) { return cb(null, "hi"); }'), reservedConcurrentExecutions: 100, }); ``` See [the AWS documentation](https://docs.aws.amazon.com/lambda/latest/dg/concurrent-executions.html) managing concurrency. ## AutoScaling You can use Application AutoScaling to automatically configure the provisioned concurrency for your functions. AutoScaling can be set to track utilization or be based on a schedule. To configure AutoScaling on a function alias: ```ts import * as autoscaling from '@aws-cdk/aws-autoscaling'; declare const fn: lambda.Function; const alias = new lambda.Alias(this, 'Alias', { aliasName: 'prod', version: fn.latestVersion, }); // Create AutoScaling target const as = alias.addAutoScaling({ maxCapacity: 50 }); // Configure Target Tracking as.scaleOnUtilization({ utilizationTarget: 0.5, }); // Configure Scheduled Scaling as.scaleOnSchedule('ScaleUpInTheMorning', { schedule: autoscaling.Schedule.cron({ hour: '8', minute: '0'}), minCapacity: 20, }); ``` [Example of Lambda AutoScaling usage](test/integ.autoscaling.lit.ts) See [the AWS documentation](https://docs.aws.amazon.com/lambda/latest/dg/invocation-scaling.html) on autoscaling lambda functions. ## Log Group Lambda functions automatically create a log group with the name `/aws/lambda/<function-name>` upon first execution with log data set to never expire. The `logRetention` property can be used to set a different expiration period. It is possible to obtain the function's log group as a `logs.ILogGroup` by calling the `logGroup` property of the `Function` construct. By default, CDK uses the AWS SDK retry options when creating a log group. The `logRetentionRetryOptions` property allows you to customize the maximum number of retries and base backoff duration. *Note* that, if either `logRetention` is set or `logGroup` property is called, a [CloudFormation custom resource](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-cfn-customresource.html) is added to the stack that pre-creates the log group as part of the stack deployment, if it already doesn't exist, and sets the correct log retention period (never expire, by default). *Further note* that, if the log group already exists and the `logRetention` is not set, the custom resource will reset the log retention to never expire even if it was configured with a different value. ## FileSystem Access You can configure a function to mount an Amazon Elastic File System (Amazon EFS) to a directory in your runtime environment with the `filesystem` property. To access Amazon EFS from lambda function, the Amazon EFS access point will be required. The following sample allows the lambda function to mount the Amazon EFS access point to `/mnt/msg` in the runtime environment and access the filesystem with the POSIX identity defined in `posixUser`. ```ts import * as ec2 from '@aws-cdk/aws-ec2'; import * as efs from '@aws-cdk/aws-efs'; // create a new VPC const vpc = new ec2.Vpc(this, 'VPC'); // create a new Amazon EFS filesystem const fileSystem = new efs.FileSystem(this, 'Efs', { vpc }); // create a new access point from the filesystem const accessPoint = fileSystem.addAccessPoint('AccessPoint', { // set /export/lambda as the root of the access point path: '/export/lambda', // as /export/lambda does not exist in a new efs filesystem, the efs will create the directory with the following createAcl createAcl: { ownerUid: '1001', ownerGid: '1001', permissions: '750', }, // enforce the POSIX identity so lambda function will access with this identity posixUser: { uid: '1001', gid: '1001', }, }); const fn = new lambda.Function(this, 'MyLambda', { // mount the access point to /mnt/msg in the lambda runtime environment filesystem: lambda.FileSystem.fromEfsAccessPoint(accessPoint, '/mnt/msg'), runtime: lambda.Runtime.NODEJS_12_X, handler: 'index.handler', code: lambda.Code.fromAsset(path.join(__dirname, 'lambda-handler')), vpc, }); ``` ## Singleton Function The `SingletonFunction` construct is a way to guarantee that a lambda function will be guaranteed to be part of the stack, once and only once, irrespective of how many times the construct is declared to be part of the stack. This is guaranteed as long as the `uuid` property and the optional `lambdaPurpose` property stay the same whenever they're declared into the stack. A typical use case of this function is when a higher level construct needs to declare a Lambda function as part of it but needs to guarantee that the function is declared once. However, a user of this higher level construct can declare it any number of times and with different properties. Using `SingletonFunction` here with a fixed `uuid` will guarantee this. For example, the `LogRetention` construct requires only one single lambda function for all different log groups whose retention it seeks to manage. ## Bundling Asset Code When using `lambda.Code.fromAsset(path)` it is possible to bundle the code by running a command in a Docker container. The asset path will be mounted at `/asset-input`. The Docker container is responsible for putting content at `/asset-output`. The content at `/asset-output` will be zipped and used as Lambda code. Example with Python: ```ts new lambda.Function(this, 'Function', { code: lambda.Code.fromAsset(path.join(__dirname, 'my-python-handler'), { bundling: { image: lambda.Runtime.PYTHON_3_9.bundlingImage, command: [ 'bash', '-c', 'pip install -r requirements.txt -t /asset-output && cp -au . /asset-output' ], }, }), runtime: lambda.Runtime.PYTHON_3_9, handler: 'index.handler', }); ``` Runtimes expose a `bundlingImage` property that points to the [AWS SAM](https://github.com/awslabs/aws-sam-cli) build image. Use `cdk.DockerImage.fromRegistry(image)` to use an existing image or `cdk.DockerImage.fromBuild(path)` to build a specific image: ```ts new lambda.Function(this, 'Function', { code: lambda.Code.fromAsset('/path/to/handler', { bundling: { image: DockerImage.fromBuild('/path/to/dir/with/DockerFile', { buildArgs: { ARG1: 'value1', }, }), command: ['my', 'cool', 'command'], }, }), runtime: lambda.Runtime.PYTHON_3_9, handler: 'index.handler', }); ``` ## Language-specific APIs Language-specific higher level constructs are provided in separate modules: * `@aws-cdk/aws-lambda-nodejs`: [Github](https://github.com/aws/aws-cdk/tree/master/packages/%40aws-cdk/aws-lambda-nodejs) & [CDK Docs](https://docs.aws.amazon.com/cdk/api/latest/docs/aws-lambda-nodejs-readme.html) * `@aws-cdk/aws-lambda-python`: [Github](https://github.com/aws/aws-cdk/tree/master/packages/%40aws-cdk/aws-lambda-python) & [CDK Docs](https://docs.aws.amazon.com/cdk/api/latest/docs/aws-lambda-python-readme.html) ## Code Signing Code signing for AWS Lambda helps to ensure that only trusted code runs in your Lambda functions. When enabled, AWS Lambda checks every code deployment and verifies that the code package is signed by a trusted source. For more information, see [Configuring code signing for AWS Lambda](https://docs.aws.amazon.com/lambda/latest/dg/configuration-codesigning.html). The following code configures a function with code signing. ```ts import * as signer from '@aws-cdk/aws-signer'; const signingProfile = new signer.SigningProfile(this, 'SigningProfile', { platform: signer.Platform.AWS_LAMBDA_SHA384_ECDSA, }); const codeSigningConfig = new lambda.CodeSigningConfig(this, 'CodeSigningConfig', { signingProfiles: [signingProfile], }); new lambda.Function(this, 'Function', { codeSigningConfig, runtime: lambda.Runtime.NODEJS_12_X, handler: 'index.handler', code: lambda.Code.fromAsset(path.join(__dirname, 'lambda-handler')), }); ```